In general, a male clamp member such as a bolt, a screw, etc. is fastened to a work by means of a female clamp member such as a wrench, a driver, etc. At this time, it is important to cause effective transmission of torque between the male clamp member (located radially inside) and the female clamp member (located radially outside).
To this end, the conventional torque transmission unit employs a male clamp member with a hexagonal head portion and a female clamp member with a socket portion of a similar shape to the head portion, or employs a female clamp member with a cross-shaped groove and a male clamp member with a corresponding cross-shaped projection.
In the conventional clamp method, however, application of excessive torque may well round a corner portion of the male clamp member and/or a groove portion of the female clamp member.
This is because there is a clearance for fitting between engaging surfaces of the male and female clamp members. The clearance permits slight rotation of the male clamp member in the female clamp member, resulting in, for example, concentration of a clamp force on a corner portion of the male clamp member. As a result, the corner portion will be rounded or deformed. Such rounding or deformation will interrupt effective transmission of torque.
Moreover, while the male clamp member rotates in the female clamp member, the axis of rotation of the former may well deviate from that of the latter. In such a state, torque cannot uniformly be applied to the clamp members, with the result that even a relatively small amount of torque may round a corner portion, etc. of the male clamp member, thereby interrupting effective transmission of torque.
Thus, in the conventional torque transmission unit, it is necessary to perform clamping while adjusting the amount of torque so as not to damage the clamp members.
The present invention has been developed in light of the above-described circumstances, and aims to provide a torque transmission unit capable of transmitting a large amount of torque without greatly damaging male and female clamp members incorporated therein.